The publication, SAE Paper 92 24 89, "Brake by Wire for Commercial Vehicles", describes an electrically regulated braking system for a vehicle, in which the braking system of a trailer or semitrailer can be controlled in an open or closed loop via a suitable interface. In such vehicle combinations, the forces occurring between the subvehicles, especially in the longitudinal direction when braking the vehicle combination are of particular importance, since they can influence travel comfort and safety. The goal of the open or closed loop control of the braking systems of such a vehicle combination is to minimize these forces. It has been found that different brake hystereses of the subvehicles, i.e. different application and release of the brakes of the subvehicles, contribute considerably to the occurrence of longitudinal forces during the braking process. Therefore, in the past, conventional devices sought to determine the application and/or release of the brakes of the subvehicles.
Thus, for example, German Application No. 41 12 845 A1 describes a compressed-air braking system in which the application and the associated controlled variable of the individual wheel brakes are determined by analyzing the time-related pressure characteristic in response to a brake actuation. Furthermore, German Application No. 195 218 72 describes a procedure according to which the application and/or release of the brakes of the trailer and semitrailer, respectively, can be determined by identification in response to braking-force build-up and braking-force reduction. Such measures make it possible to derive the controlled variables to be preset for the application and/or release of the wheel brakes of the subvehicles of a vehicle combination.
Taking these variables into account in the control of the braking systems contributes to considerable improvement in the braking performance. Using conventional methods, the longitudinal forces between the vehicle sections of a vehicle combination can be effectively controlled and reduced. However, the procedure in conventional methods require too much effort, and a relatively long time is needed until reliable results of the identification are available.
An object of the present invention is to specify measures, by which the longitudinal forces between the subvehicles of a vehicle combination can be minimized quickly and reliably.